1. Transaction Management
Chapters 20
Transaction Management

2. Agenda Properties of Transaction Concurrent Processing
Database Protection
Recovery

3. Property of Transactions (ACID)
Atomicity
Consistency
Isolation
Durability

4. Concurrent Processing
Definition
Problems
Control

5. Concurrent Processing
Multiprogramming
Interleaved between two transactions
CPU
I/O
Logical unit of work

6. Concurrent Processing Problem
No problem
Write different data
Update different data
Read the same data
Problem
Write the same data
Update the same data

7. Concurrent Processing Problems
Lost update
Two transactions simultaneously update the same files
Uncommitted update
Transaction 2 uses the result updated by transaction 1
Transaction 1 aborts and rolls back
Transaction 2 commits
Inconsistent Analysis
Transaction 1 reads
Transaction 2 reads and uses for calculation
Transaction 1 updates and commits
Transaction 2 updates and commits

8. SERIALIZABILITY
Transaction results form concurrent processing are the same as if stand-alone sequential processing was used
Ensure no anomalies arise from concurrent processing

9. Concurrency Control Locking Deadlock Two-phase locking Timestamping
Optimistic technique

10. Locking Types Granularity Shared Locks vs. Exclusive Locks
Read Locks vs. Write Locks
Upgrade vs. Downgrade
Granularity
Database
file
page
record
field

11. Deadlock Definition Control
Tow or more transactions each wait for locks held by other transaction
Livelock
Control
Wait-Die
Wound-wait

12. Two-phase Locking Growing phase Shrinking phase Get all locks
Upgrade locks
Shrinking phase
Downgrade locks
Once starting to release a lock - no more new locks

13. Timestamping Timestamp Timestamp protocol
unique identifier as relative starting time of a transaction
Read-timestamp & write timestamp
Timestamp protocol
Transactions with smaller timestamps get priority in the event of conflict
Transaction is only allowed on the item with smaller read-timestamp or write timestamp

14. Optimistic Technique
Read phase
Validate phase
Write phase

15. Database Recovery
Restoring the database to its correct state in the event of a failure
Why?
Physical (fire, flood, etc.)
Sabotage
Carelessness
Hardware
Software (application/system)

16. Database Protection Back up Transaction log Checkpoint
Copy of the database
Transaction log
Transaction ID, time, operation, object, before image, after image, prior pointer, next pointer
Checkpoint
Synchronize transaction log and the database
Write data from buffers to database on the disk
Write checkpoint to log identify current transaction(s)

17. Recovery Methods Reprocessing Rollforward Rollback
Record all transactions since last backup and replay those transactions
Rollforward
Use the transaction log to change any committed transactions on the database or since last checkpoint
Rollback
Use transaction log to undo any aborted transactions

18. Shadow Paging Method Current page table vs. Shadow page table
Pros & cons
Faster
Less overhead
Data fragmentation
Reclaim inaccessible blocks

19. Failure & Recovery Aborted transaction Incorrect data System failure
Rollback
Incorrect data
Rollback or restart from checkpoint
System failure
Database destroyed
Rollforward from last backup

20. Points To Remember Properties of Transaction Concurrent Processing
Database Protection
Recovery

21. Assignments Review chapters 5-6, 11-13, 18-19, 24-26 Exam 3 Project
Date: 5/13/04
Project
Due date: 5/20/04
Place: MIS Department Office

22. End of MIS150 Exam date: 5/13/03 Study! Study! Study!
Have a happy and safe holiday!!